Influenza activity in Canada is starting to decline
During week 16, overall influenza activity in Canada continued to decline. Only 1 region reported widespread influenza activity (in ON). Localized influenza activity was reported by 16 regions, 8 regions reported no activity and 29 reported sporadic activity (see map). In week 16, the percentage of specimens that tested positive for influenza declined to 16.8% (758/4,517) for Canada as a whole with the majority of the provinces having reported percentages below 15% except NS (34%), BC (31%) and ON (27%) (see table). To date this season, 59.7% of influenza detections in Canada were for influenza A viruses and 40.3% were for influenza B viruses. This week, the ILI consultation rate was 24 ILI consultations per 1,000 patient visits (see ILI graph), which is slightly above the expected range for this week. The sentinel response rate was 50%. Fourteen new outbreaks of influenza or ILI were reported this week as follows: 7 LTCFs, 1 hospital, 3 others and 3 schools.

Antigenic Characterization:
The National Microbiology Laboratory (NML) has characterized 1,149 influenza viruses for the 2007-2008 influenza season: 449 (39%) A(H1N1), 164 (14%) A(H3N2) and 536 (47%) B viruses. Of the 449 influenza A(H1N1) viruses characterized, 429 (96%) were antigenically similar to A/Solomon Islands/3/2006 and 20 (4%) were antigenically similar to A/Brisbane/59/2007. Of the 164 influenza A(H3N2) viruses characterized, 7 (4%) were antigenically similar to A/Wisconsin/67/2005 and 157 (96%) were antigenically similar to A/Brisbane/10/2007. One of the 6 A/Wisconsin-like viruses had reduced titer to A/Wisconsin/67/2005 reference antiserum. Of the 536 influenza B isolates characterized, 8 (1%) were antigenically similar to B/Malaysia/2506/2004 and 528 (99%) were antigenically similar to B/Florida/4/2006 (belonging to the B/Yamagata lineage) (see pie chart).

***The WHO recommends that the vaccines to be used in the 2008-2009 season (northern hemisphere) contain the following: an A/Brisbane/59/2007 (H1N1)-like virus; an A/Brisbane/10/2007 (H3N2)-like virus; and a B/Florida/4/2006-like virus.

• WHO

Antiviral Resistance:
Since the start of the season, the NML has tested 833 influenza A isolates (521 H1N1 and 312 H3N2) for amantadine resistance and found that 310 (99%) of the 312 H3N2 isolates were resistant to amantadine and 5 (1%) of 521 H1N1 isolates were resistant (see recommendation from the 2006-2007 influenza season below).

The NML has also tested 1,105 influenza isolates (460 A/H1N1, 157 A/H3N2 & 488 B) for oseltamivir (Tamiflu) resistance and found that 112 (24.3%) of the 460 H1N1 isolates tested were resistant to oseltamivir. The resistant isolates were from NL, NS, NB, QC, ON, MB, AB and BC. Of the 112 resistant viruses, 108 were A/Solomon Islands/3/06/-like and 4 were A/Brisbane/59/07-like. These oseltamivir resistant strains remain sensitive to the antiviral amantadine.

Influenza-associated Paediatric Hospitalizations:
In week 16, there were 16 new laboratory-confirmed influenza-associated paediatric hospitalizations reported through the Immunization Monitoring Program Active (IMPACT) network from AB, ON, QC, NS and NL of which 11 (69%) were due to influenza A. Of the 417 hospitalizations reported so far this season, 63% (263/417) have been due to influenza A. The proportion of cases to date by age group are as follows: 20% were 0-5 month olds; 26% were 6-23 month olds; 23% were 2-4 year-olds; 21% were 5-9 year-olds; and 10% were 10-16 year-olds. Since the start of the season, 1 influenza-associated pediatric death has been reported to PHAC.

International:

WHO: During weeks 14–15, the level of overall influenza activity in the world decreased. Countries in the northern hemisphere reported reduced activity. Some detections of influenza A (predominantly H1N1) viruses still occurred.

• WHO

CDC: During week 15, influenza activity continued to decrease in the United States with most influenza indicators having decreased from the previous week. Since September 30, 2007, CDC antigenically characterized 620 influenza viruses: 290 influenza A(H1) (200 A/Solomon Islands/3/2006-like, 20 showed somewhat reduced titers with antisera produced against A/Solomon Islands, and 70 were A/Brisbane/59/2007-like), 161 influenza A(H3) (35 A/Wisconsin/67/2005-like, 115 A/Brisbane/10/2007-like and 11 showed somewhat reduced titers with antisera produced against A/Wisconsin and A/Brisbane), and 169 influenza B viruses (8 belonging to the B/Victoria and 161 B/Yamagata lineage). Small numbers of influenza viruses resistant to oseltamivir have been detected in the United States, representing 7.3% (87/1,195) of all influenza viruses tested (10.4% among H1N1 viruses tested). To date, CDC has received a total of 66 reports of influenza-associated pediatric deaths that occurred this season.

• CDC

EISS: Seasonal influenza activity is now back to levels seen outside the winter period in all European countries. Influenza activity was predominantly caused by the A(H1N1) influenza virus during most of the season and influenza B has been dominant in Europe since week 09/2008. In most countries, influenza activity only reached moderate levels of intensity this winter. Influenza A(H1N1) viruses resistant to oseltamivir have been found in 19 countries in Europe with an overall prevalence of 23% (586/2533).

• EISS

Recommendation for the Use of Amantadine for Treatment and Prevention of Influenza
The Public Health Agency of Canada does not recommend the use of amantadine for treatment or prevention of influenza for the 2006-2007 season. This recommendation will be revisited if new information becomes available.

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Total number of influenza tests performed and number of positive tests by province/territory of testing laboratory, Canada, 2007-2008

Province of reporting laboratories	Report Period: April 13 to April 19, 2008				Season to Date: August 26, 2007 to April 19, 2008
	Total # Influenza Tests	# of Positive Tests			Total # Influenza Tests	# of Positive Tests
		Influenza A	Influenza B	Total		Influenza A	Influenza B	Total
NL	65	6	2	8	1129	69	124	193
PE	13	0	1	1	138	2	19	21
NS	65	8	14	22	883	93	84	177
NB	79	2	7	9	1184	102	163	265
QC	1424	79	135	214	26120	2087	913	3000
ON	1625	214	229	443	30010	2198	1332	3530
MB	58	0	0	0	2579	80	33	113
SK	177	7	3	10	5552	338	276	614
AB	933	21	6	27	27297	872	910	1782
BC	78	14	10	24	3347	547	456	1003
Canada	4517	351	407	758	98239	6388	4310	10698

 

Specimens from NT, YT, and NU are sent to reference laboratories in other provinces.

Note: Cumulative data includes updates to previous weeks; due to reporting delays, the sum of weekly report totals do not add up to cumulative totals.

Abbreviations: Newfoundland/Labrador (NL), Prince Edward Island (PE), New Brunswick (NB), Nova Scotia (NS), Quebec (QC), Ontario (ON), Manitoba (MB), Saskatchewan (SK), Alberta (AB), British Columbia (BC), Yukon (YT), Northwest Territories (NT), Nunavut (NU)

Respiratory virus laboratory detections in Canada, by geographic regions, are available weekly on the following website:
<http://www.phac-aspc.gc.ca/bid-bmi/dsd-dsm/rvdi-divr/index-eng.php>

Number of influenza surveillance regions† reporting widespread or localized influenza activity, Canada, by report week, 2007-2008 (N=54)

† sub-regions within the province or territory as defined by the provincial/territorial epidemiologist. Graph may change as late returns come in.

Influenza Activity Level by Provincial and Territorial Influenza Surveillance Regions, Canada, April 13 to April 19, 2008 (Week 16)
	No Data No Activity Sporadic Activity Localized Activity Widespread Activity

Note: Influenza activity levels, as represented on this map, are assigned and reported by Provincial and Territorial Ministries of Health, based on laboratory confirmations, sentinel ILI rates (see graphs and tables) and outbreaks. Please refer to detailed definitions. For areas where no data is reported, late reports from these provinces and territories will appear on the FluWatch website. Select single maps by report week to get this updated information.
<http://dsol-smed.phac-aspc.gc.ca/dsol-smed/fluwatch/fluwatch.phtml?lang=e>

Click on the map to view provinces/territories and maps for other weeks.

Influenza tests reported and percentage of tests positive, Canada, by report week, 2007-2008

 

Percent positive influenza tests, compared to other respiratory viruses, Canada, by reporting week, 2007-2008

Influenza strain characterization, Canada, cumulative, 2007-2008 influenza season by the Respiratory Viruses Section at the National Microbiology Laboratory
[N=1,149]

{Strain characterization, number identified, per cent of total number}

NACI recommends that the trivalent vaccine for the 2007-2008 season in Canada contain A/Solomon Islands/3/2006 (H1N1)-like virus; an A/Wisconsin/67/2005 (H3N2)-like virus; and a B/Malaysia/2506/2004-like virus.

Influenza-like illness (ILI) consultation rates, Canada, by report week, 2007-2008 compared to 1996/97 through to 2006/07 seasons

Note: No data available for mean rate in previous years for weeks 19 to 39 (1996-1997 through 2002-2003 seasons).

Number of New Outbreaks in Long Term Care Facilities, Canada, by Report Week, 2007-2008

Please note that the above graphs may change as late returns come in.

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Definitions for the 2007-2008 season